Simply choose the Uninstall item from the "SwitchResX Control" menu in the SwitchResX Control application, and all components will be removed. Note that SwitchResX itself is not removed from your computer at this point, and you will have to remove the preferences pane from MacOS X manually (check here for example).

If you can't find the item, look the following picture:

If you still can't find it, you may have installed SwitchResX 3 instead, and you'd better look at this page in this case